The prior art teaches the formation of integrated circuits which utilize one or more FinFET type field effect transistors. The FinFET transistor comprises a channel region which is oriented to conduct an electrical current parallel to the surface of the substrate. The channel region is provided in an elongated section of semiconductor material referred to as a “fin”. The source and drain regions of the transistor are formed in the elongated section on either side of the channel region. A gate is placed over and on both opposed sides of the elongated section at the location of the channel region to provide control over the conductive state of the transistor. This FinFET design is well suited for manufacturing a multi-channel transistor in which multiple elongated sections are formed in parallel to define neighboring channel regions which are separated from each other by an intermediate gate portion of the transistor gate spanning with a perpendicular orientation over the multiple elongated sections.
To avoid leakage currents, it is known in the art to fabricate the FinFET transistor on an integrated circuit substrate which is of the Silicon-on-Insulator (SOI) type. Such an SOI substrate comprises, in a lower part, an intermediate layer of electrically insulating material which is topped by a crystalline silicon layer. Reference is made to U.S. Pat. No. 6,645,797, the disclosure of which is incorporated by reference, which teaches a process for realizing a FinFET transistor from an SOI substrate. The transistor which is obtained is electrically insulated from the lower part of the substrate by the intermediate layer of insulating material, and thus leakage current concerns are reduced.
The FinFET transistor implemented on an SOI substrate is considered by those skilled in the art as an attractive option for use in connection with circuits fabricated at aggressively scaled process technology nodes, and in particular is well suited for use in CMOS integrated circuit designs. Superior short channel control along with higher performance in comparison to conventional planar bulk devices are recognized as advantages associated with the selection of the FinFET for CMOS circuits.
However, as CMOS process technology continues to scale towards smaller and smaller dimensions, further improvement in transistor performance is needed. Those skilled in the art recognize that the use of silicon-germanium (SiGe) materials for transistor fabrication provide for a significant boost in transistor performance, especially with respect to p-channel field effect transistor devices. Indeed, the art is moving towards the use of SiGe for p-channel devices implemented in both bulk device technology and SOI technology. Specific to the use of FinFET devices, those skilled in art recognize a need to form the fin of the p-channel device from a SiGe material in order to reach improved transistor performance levels over prior art Si material only devices.
The formation of a SiGe fin for a FinFET device is not without challenge. Fabrication techniques known in the art for SiGe fabrication use an extensive thermal budget. These thermal treatments can cause germanium to diffuse from the substrate regions where p-channel devices are being fabricated. This is of particular concern in connection with the fabrication of CMOS circuitry as the Ge from the SiGe material may diffuse into the adjacent substrate regions where n-channel devices are being fabricated and adversely affect the performance of the n-channel devices. To address the issue of Ge diffusion, a different fabrication technique forms the SiGe fins (for the p-channel devices) after the Si fins (for the n-channel devices) have been defined. However, such devices suffer from a concern over non-uniform fin shape due to the difficulty of forming a uniform SiGe epitaxy around the fin.
There is accordingly a need in the art for a fin fabrication process that does not suffer from the foregoing problems.